1. Field of the Invention
The present invention relates to a hydrodynamic bearing device used in a spindle motor such as a small HDD (Hard Disc Drive) motor of, for example, not more than one inch, a spindle motor including the hydrodynamic-bearing device, and a recording and reproducing apparatus mounted with the spindle motor.
2. Description of the Related Art
In recent years, with entry of HDDs into AV (Audio Visual) products and home electrical products, the spindle motors are required to be compact, thin, highly accurate and have long life spans. In FIG. 10 showing a configuration of the spindle motor 57, a sleeve 52 is provided on a base 51, a rotating shaft 53 is inserted into the sleeve 52, and a hub 54 for receiving a disc 65 is attached to a distal end of the rotating shaft 53, which hub 54 is provided with a magnet 55. A stator 56 wound with coil is provided facing the inner peripheral side of the magnet 55.
The hydrodynamic bearing is adopted as the bearing for higher accuracy and longer life span of the spindle motor 57. That is, a thrust plate 58 that receives a thrust load acting on the rotating shaft 53 is provided at the lower end portion of the sleeve 52. A flange part 59 having a diameter larger than the rotating shaft 53 is provided at the far end portion of the rotating shaft 53. The flange part 59 prevents the rotating shaft 53 from slipping out upward from the sleeve 52 and configures the thrust bearing.
An operating oil which is an operating fluid is filled to each of a gap 60a formed between the outer peripheral surface of the rotating shaft 53 and the inner peripheral surface of the sleeve 52, a gap 60b formed between the outer peripheral surface of the flange part 59 and the inner peripheral surface of the sleeve 52, a gap 60c formed between an upper surface of the flange part 59 and a lower surface of the sleeve 52 facing the upper surface of the flange part 59, and a gap 60d formed between the lower surface of the flange part 59 and the upper surface of the thrust plate 58.
A pair of upper and lower radial bearing parts 62a and 62b formed with a dynamic pressure generating groove are provided in a direction of the shaft center at the inner peripheral surface of the sleeve 52. A main thrust bearing part 63 formed with the dynamic bearing groove is provided on the upper surface of the thrust plate 58. An auxiliary thrust bearing part (not shown) formed with the dynamic bearing groove is provided on the upper surface of the flange part 59. In the spindle motor 57 configured as above, the rotating shaft 53 rotates and further the hub 54 rotates by sequentially energizing the coil.
However, the height limit of the motor 57 is becoming more severe to miniaturize and thin the motor 57. With the hydrodynamic bearing of the shaft rotation type motor 57 shown in FIG. 10, the formable height H of the radial bearing parts 62a and 62b is reduced by the thickness of the flange part 59 due to the arrangement of the flange part 59 to prevent slip out. Therefore, the spacing S (span) in the vertical direction between the upper (one) radial bearing part 62a and the lower (other) radial bearing part 62b and the bearing length are shortened without being sufficiently secured, thereby lowering the stiffness with respect to impact.
FIG. 10 shows the shaft rotation type motor 57, whereas FIG. 11 shows the shaft fixed type motor. A bracket 71 is provided upright on the fixed shaft 72. A freely rotating rotor hub 73 that receives the disc 80 is externally fitted to the fixed shaft 72. A ring shaped member 74 for preventing the rotor hub 73 from slipping out upward from the fixed shaft 72 is attached to the upper end portion of the fixed shaft 72.
Lubricating oil 76 which is the operating fluid is filled into a space 75a formed between the inner peripheral surface of the rotor hub 73 and the outer peripheral surface of the fixed shaft 72, and a space 75b formed between the lower end face of the rotor hub 73 and the upper surface of the bracket 71. A radial bearing part 77 formed with the dynamic pressure generating groove is provided on the inner peripheral surface of the rotor hub 73. A thrust bearing part 78 formed with the dynamic pressure generating groove is provided on the lower end face of the rotor hub 73. Further, a magnet 82 is attached to the rotor hub 73. In the spindle motor configured as above, the rotor hub 73 rotates by sequentially energizing the coil of the stator 81.
However, in the hydrodynamic bearing device of the shaft fixed type motor 79 shown in FIG. 11, the formable height H of the radial bearing part 77 is reduced by the thickness of the ring shaped member 74 due to the arrangement of the ring shaped member 74 to prevent slip out, thereby lowering the stiffness with respect to vibration and impact.